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Narrow ribs of dirt and rock beneath Antarctic glaciers help slow the glaciers' flow into the sea, according to new research from scientists at Princeton University and the British Antarctic Survey. Using satellite measurements of the Pine Island Glacier and Thwaites Glacier, both in West Antarctica, researchers discovered bands they call "tiger stripes" underlying the glaciers. The stripes serve as zones of friction and prevent sliding, much like non-slip flooring, the researchers report in Science. Understanding the factors that control the glaciers' flow to the sea is important because their melting contributes significantly to sea level rise. The Pine Island and Thwaites glaciers are particularly important, as together they've contributed about 10 percent of the observed global sea level rise over the past 20 years, with the Pine Island Glacier moving at a rate of 1.5 miles per year. The so-called tiger stripes may be related to drumlins — raised bands of rock and soil that were deposited by glaciers long ago.